Re: [PATCH v9 10/13] cxl: Enable AMD Zen5 address translation using ACPI PRMT

[Jonathan Cameron]

On Wed, 14 Jan 2026 16:21:03 +0100
Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:

> On Wed, 14 Jan 2026 at 15:00, Robert Richter <rrichter@xxxxxxx> wrote:
> >
> > On Wed, Jan 14, 2026 at 08:47:22AM +0100, Ard Biesheuvel wrote:  
> > > (cc Peter)
> > >
> > > On Sat, 10 Jan 2026 at 12:46, Robert Richter <rrichter@xxxxxxx> wrote:  
> > > >
> > > > Add AMD Zen5 support for address translation.
> > > >  
> > > ...  
> > > > Do the following to implement AMD Zen5 address translation:
> > > >
> > > > Introduce a new file core/atl.c to handle ACPI PRM specific address
> > > > translation code. Naming is loosely related to the kernel's AMD
> > > > Address Translation Library (CONFIG_AMD_ATL) but implementation does
> > > > not depend on it, nor it is vendor specific. Use Kbuild and Kconfig
> > > > options respectively to enable the code depending on architecture and
> > > > platform options.
> > > >
> > > > AMD Zen5 systems support the ACPI PRM CXL Address Translation firmware
> > > > call (see ACPI v6.5 Porting Guide, Address Translation - CXL DPA to
> > > > System Physical Address). Firmware enables the PRM handler if the
> > > > platform has address translation implemented. Check firmware and
> > > > kernel support of ACPI PRM using the specific GUID. On success enable
> > > > address translation by setting up the earlier introduced root port
> > > > callback, see function cxl_prm_setup_translation(). Setup is done in
> > > > cxl_setup_prm_address_translation(), it is the only function that
> > > > needs to be exported. For low level PRM firmware calls, use the ACPI
> > > > framework.
> > > >  
> > >
> > > Does the PRM service in question tolerate being invoked unprivileged?
> > > The PRM spec requires this, and this is something we may need to
> > > enforce at some point.
> > >
> > > cc'ing Peter with whom I've discussed this just recently.  
> >
> > Interesting appoach, need to check if that works. I haven't tried that
> > yet. Though, that needs some rework of the kernel code as some high
> > priority code depends on the translation and that would cause kind of
> > priority inversion. E.g. an interrupt handler cannot wait until a
> > dpa-to-spa conversion is done.
> >  
> 
> This is not about running it in user space, but about running the code
> in an unprivileged sandbox. So scheduling wpuldn't really come into
> play here.

Hi Ard,

I haven't looked into the background yet, so a naive question:

Do we have a potential issue wrt to merging this as it stands and improving
on it later?  i.e. Is this a blocking issue for this patch set?

Thanks,

Jonathan

> 
> > For CXL it is only used for region setup in the init path and process
> > context. For tracing and error handling those translations are
> > disabled. See patch 13/13.
> >  
>